Filter sequencing for mono CCD

[sadia]

Hello,

I will be trying some mono soon to see how I go with mono compared to OSC. There are few good articles that i am going through at the moment but most of them are mainly talking about on processing part and how to make LRGB. I was wondering if someone could tell me or give me a link on how they plan the sequencing of their LRGB filters with a mono CCD. Things like whether you take frames in LRGB, LRGB, LRGB sequence all the time or would you plan to Take specific filter lights for specific altitude (R low altitude compared to Blue high altitude)?

Regards
Sad

[AlexN]

You want your Luminance data taken during the best possible seeing conditions, so I'll be taking Lum frames at say 70° minimum altitude through to the meridian, flip the mount then shoot Lum in the West down to about 70°.. RGB data I plan to shoot RGB,RGB,RGB,RGB from say 45°~50° through to 70°, and from 70° back down to 50° ~ 45°

If shooting one target for consecutive nights, I might shoot Lum for 2.5 nights straight from 50° flip the mount at the meridian and shoot lum's back down in the west to about 50°, then on the final night shoot Lum to zenith, then shoot RGB, RGB, RGB from the meridian down to 40° or there abouts...

Colour data is not particularly important.. Well, its important obviously, but the quality of the data is not so much. Ie. A lot of imagers will bin colour exposures 2x2, as the resolution/detail just dont matter. Think of it in art terms, your luminance filter is essentially a fine liner pen. Its great for detail, but its just black and white.. your colour is like a box of crayons... it doesnt have to be detailed.... it just has to be colourful.

I've been looking recently, I've found some stunning images on line that come from hours and hours and hours of luminance images, and 3x5min R, G and B.... Just 45mins total colour exposure for anywhere between 10 and 25 hours of Lum...


A few people I know like to shoot LRGB, LRGB, LRGB all night, as this way you're always guaranteed a colour image at the end of the night. I dare say it would be VERY annoying to get 4 hours of luminance, 3x5 mins through the red filter, 2x5 mins through the green then get swamped by clouds... Something to keep in mind.

[Paul Haese]

I am certainly not an authority on this subject but the way I image is like this. One night I shoot my colour. I like lots of data in the colour (usually around 90-110 minutes in each colour). I then focus the remaining nights on getting luminence and Ha which are my detail components. I image from about 40 degrees up in all imaging components. My recent tarantula image took 3 nights to get all the data.

To get scope back into the same position each night I use a grid over the viewing panel of my guide star. I simply put the star into the same position and this affords me good registration.

Hope that helps and best of luck with mono imaging.

[AlexN]

As far as lining up the second night, you can do it the way Paul mentioned if you dont have a lot of guide stars in the field of view that look the same... Taking a screenshot of the guider window might help in that regard.

What I do is open one of the images from the previous night in CCDSoft or Maxim, then take a new exposure.. Using the "blink" function, you can have the software blink between the image from the previous night and the current image. this way you can line it all up very precisely.. to the point of having all the stars within a few pixels from night to night... Clearly, this is less important with a very wide field of view, but with a narrow imaging setup like Paul's RC, it is pivotal..

[Bassnut (Fred)]

Originally Posted by Paul Haese

I am certainly not an authority on this subject but the way I image is like this. One night I shoot my colour. I like lots of data in the colour (usually around 90-110 minutes in each colour). I then focus the remaining nights on getting luminence and Ha which are my detail components. I image from about 40 degrees up in all imaging components. My recent tarantula image took 3 nights to get all the data.

To get scope back into the same position each night I use a grid over the viewing panel of my guide star. I simply put the star into the same position and this affords me good registration.
Hope that helps and best of luck with mono imaging.

Thats interesting, I think the reverse

Lum is critical, without it your dead, its where all the detail is, so I take Lum 1st (Ha actually, Ha RGB is way better, for nebs anyway), to get started, if that doesnt work, move on .

Once thats looking good, sneak in RGB between lum subs, and if your lum is looking really good, do RGB at the end. Always do lum if the seeing is tops on the night.

You can get away with really crap RGB with LRGB, youd be supprised how bad RGB you can get away with at a pinch with good Lum.

This assumes you have the time to do mega data, if not spread L and RGB on a 3 to one ratio, ie 3 lum, R, 3 lum, G, 3 lum, B, ....repeat untill you run out of time. That way you have something to fiddle with if it all goes pear shaped

[AlexN]

Originally Posted by Bassnut

This assumes you have the time to do mega data, if not spread L and RGB on a 5 to one ratio, ie 5 lum, R, 5 lum, G, 5 lum, B, ....repeat untill you run out of time. That way you have something to fiddle with if it all goes pear shaped

My comments also assumed at least one full night for one target...

If you were doing a quickie, then doing 5:1 LRGB exposures as fred mentioned.. Thats the way to go to ensure getting an image..

[sadia]

Thank you guys. I will keep in mind whats been suggested and wait for the ccd & filters.

[Paul Haese]

Fred, you are right, what I meant was I devote several nights to either Lum or Ha or RGB. My Tarantula I did 4 nights worth of imaging to complete the image. I am quite lucky at the house as I have pretty constant 1 arc second skys. Some nights are 0.7 arc seconds. I had it tested by a chap on an average night and it was 0.7 for several hours but it averaged out at 1.0" with a DIM. I knew it was good but sub arc second is exceptional for a coastal region.